Rubber composition and preparation thereof



United States 2,944,042 Patented July 5, 1960 V RUBBER COMPOSITION AND PREPARATION THEREOF Herbert Anderson, Jr., Bartlesvilie Ok1a., assignor to Phillips Petroleum Company, a corporation of Delaware This invention relates to rubbers containing sulfides of metals selected from group VI-A of the periodic table. In one aspect, it relates .to sulfides of metals of group VI-A of the periodic table employed as a reinforcing agent in rubber compositions.

This application is a continuation-in-part of my 'copending application S.N. 600,371, filed July 27, 1956.

I have found, quite surprisingly, that natural and synthetic rubbers can be compounded with a sulfide of a metal of group VI-A of the periodic table alone or in admixture with other substances and cured (or vulcanized) to yield a product possessingdesirable modulus, tensile strength and/or elongation characteristics,

Accordingly, therefore, one or more of the followin objects will be obtained by the practice of my invention.

One object of this invention is to provide a novel rubber composition comprising a sulfide'of a metal of group VI-A of the periodic table. 7

Another object of this invention is to provide a novel rubbercomposition containing a reinforcing amount of a sulfide of a group VI-A'metal. I

A further object of this invention is to produce novel I rubbers containing a sulfide of a-groupVI-A- metal, useful for decorative purposes.

A further object of this invention is to provide novel Other objects will become apparent to those skilled in the art upon the reading of my disclosure.

Broadly, my invention relates to rubbers compounded with a reinforcing quantity of a sulfide of a group VI-A metal, such as, molybdenum sulfide (MoS), molybdenum sesquisulfide (M0 8 molybednum, disulfide (M08 molybdenum trisulfide (M98 molybdenum tetrasulfide (M08 molybdenum pentasulfide (Mo- S tungsten disulfide (W5 tungsten trisulfide (W8 uranium sulfide (US), uranium sesquisulfide (U 8 uranium disulfide (U8 chromium sulfide (CrS), chromium sesquisulfide (Cr S chromium disulfide -(CrS chromium tritetrasulfide (Cr S chromium tetraheptasulfide (Cr S and chromium hemiheptasulfide (Cr S- The preferred reinforcing agents are molybdenum disulfide and tungsten disulfide.

The group VI-A metal sulfide can be the sole reinforcing agent or it can be admixed with carbon black or a mineral pigment such as clay, silica, kaolin, calcium silicate, titanium dioxide, hydrated alumina, calcined magnesia, calcium carbonate, zinc sulfide, zinc oxide, or other conventional fillers well recognized in the art- As a practical matter, the amount of group VI A metal sulfide employed will generally be governed bythe type of product desired. The amount of sulfide required to elongation impart the desired characteristics to the finished product is readily determinable by those skilled in the rubber compounding art. Generally, when-the sulfide is utilized as the sole reinforcing agent, the amount employed will be in the range from about 25 to about 400 parts by weight per parts of rubber, preferably from about 25 to about 250. When using molybdenum disulfide and tungsten disulfide the preferred quantities are from about 25 to about 150 and from about 40 to about 250, respectively.

The group VI-A metal sulfide can be admixed with other well-known reinforcing agents such as the various carbon blacks and mineral pigments of the type illustrated above preferably in an amount wherein at least 10 percent by weight of the total reinforcing admixture is the sulfide. The total reinforcing admixture will generally be in the range of about 25 to 400, and higher, parts by weight per 100 parts of rubber, preferably from about 25 to about 250.

The rubbers applicable in this invention are natural or synthetic rubbers with Mooney values (ML-4) generally ranging from about 10-125, or higher, preferably in the range from about 10-75. The natural andsynthetic rubbers are well known to chemists skilled in the rubber art. The synthetic rubbers can be prepared in any manner known in the art, such as mass or emulsion polymerization. One suitable method is the emulsion polymerization of conjugated diolefins alone or with other copolymerizable monomers at to F. in such systems as the iron-pyrophosphate, either sugar-free or containing sugar, and the persulfate recipes. Any suitable emulsifier such as a fatty or rosin acid soap or the like can be used. These recipes-usually contain l-9 parts by Weight of the emulsifier per 100 parts of monomer.

The synthetic rubbers may be homopolyrners of iconjugateddienes or copolymers of conjugated. dienes; with a compound containing an active-CH;;==C group wh ch above diene can be rany 'monomer containing an-active CHFC group such as aryl olefins, esters of acrylic and substituted acrylic acids, nitriles, amides, ketones,

and vinylpyridines. Examples of such monomers include, among "others, styrene, '"alpha-rnethylstyr'ene," pi-chlorostyrene, p-methoxystyrene, acrylonitrile, methacrylonitrile,

methyl methacrylate, butyl methacrylate, methacrylarnide, methyl isopropenyl ketone, 2-vinylpyridine, Z-methyl- S-Vinylpyridine, 3-ethyl-5-vinylpyridine, and the like.

The group VI-A metal sulfide isincorporated into the rubber stocks as a fine powder and imparts a gray metallic appearance to the finished product. When employed as a fine powder the sulfide particles are relatively large as compared with other reinforcing agents such as the carbon blacks. The reinforcingcharacteristics of the sulfide are equivalent to the'soft carbon blacks. The smaller the sulfide particle size, the more pronounced are the reinforcing characteristics in rubber stocks. The non-porous sulfide. will generally have a surface. area greater than one square meter per gram, and preferably greater than 5 square meters per gram. The group VI-A metal sulfide containing rubbers areuseful'for decorative purposes such as molding on the dashboards of automobiles, in the homes, etc. These rubbers .are also useful as gasket stock, and in the manufacture of automobile tires.

'rubber,'e.g., in cold 'butadiene/styrene rubber, the group VI-A metal sulfides give a stock which has a higher 7' ,modulus, higher hot tensile strength and higher aged i tei isile strength-than-a similar-stock in which a carbon Ebleick having a' 'similar surface area to the sulfides =is --employed.' lt :also shows good reinforcing characteristics -in 'natural1 'ubber and hot and other types ofrubf i r p 7 e 1 Thetech :gueofcompounding'rubbersis'well known infthe' art. 'By' way" of illustration} the group VI- A metalsulfide reinforcing agent can be. incorporated into the rubber by mill mixing along with other compounding ingredients'or by alatex'masterbatching operation -vjvhercin'an aqueo us'slurry-of the mineral "pigment is ='-gen'erally prepared first and then mixed with the latex.

' After all ingredients have been incorporated into the rubber; 'the composition is vulcanized or cured by heating'for a period sufficient to cure.

The following examplesare illustrated merely to represent various embodiments of my invention, and these examples are not to be construed as limiting the scope of the invention. a 7

EXAMPLE 1.

a 75/25 butadienefistyrene. rubber was prepared by emulsion. polymerization, at 41 F. .to .give a polymerf having a raw :Mooney'value. (M11 4) of 52a'nd abound styrene content-ofZO. percent. Atypical recipe. forthe production of,a polymerzofthisItype-is-as follows: I

1 Sodium salt of a naph thaleneifeulfonic acid {condensed xvith fonnaldehyde.

] "I'heirubber was ,compoundedlusing as jreinforcing agentsmolybdenum disulfideand two difierent carbon "blacks havinga surface area- 'to' the molybdenum.

The compounding recipes were' asgfollows;

Parts byWeight Rubber 100 100 100 Molybdenum disulfide 131. 4 5

. .Thermex 1 50.

a P-33 1 s1. 7 Zinc oxide. 3' "3 3 Stearicacid 1 1 '1 Flexamine h. l 1 1 -SuJur--. l 75 V 1175 1.75 ::Santocur.e 1 1.1 1.1

..Ihewelghts-oi filler usedpr'ovided an equal rolumeln each stock (approx mately 27.8 cc. per- 100 grams rubber). 3 Medium thermal carbon black.

3 Fine thermal carbon black.

i Physiealmixture containing" 65 percent of'a complex-i diarylaminefiketone 'rac'tion produotand -35 pereent'oi N,N-diphenyl-p-phenylenemine. 'fN cyclohexyhz benzothiazylsulfenamide.

j Thevstockswere'compounded one roll mill, cured'30 "Results were as followsz Y I 7 Recipes 5 Molybdenum Thermax P-33 Disulflde' Unagedsamplesz Compression set, percent a w, 19 1 17.8 1 V 300% Modulus,p.s.i. (809T). 460 a 410 Tensile, .51. (30 n,) 1,820 2, 410 3,350 Elongation, percent (80F. "-570 I-20 785 200 F. Maximum-tensile, p; 9001 25 0; 7 300 A T, F 61.9 41 9* 44. 6 Resilience, percent 65.8 71. 9 69.3 Shore hardness- 60 v 45 48 compounded Msqy zizr 30 5 29:6 28 5 Gehman freeze point, Q. -60 51 -48 Surface area 0f-.reinf0rcm I mfi/g 7 1 7. 5 18 7 Oven Aged 24 Hours at 212 F:

300 percent Modulus, ps1.

30 F. p 1, 515 820 600 Tensile, p'.s.i. (80 F.) 1; 700.. 1; I20. :1, 160 Elongation, percent (80 F. 330 5 380 1480 A T", F;. 6618 31' 1' 36; 5 Resllleuee'percent 1722.9. 78 4 .7576

. lt is apparent that the oven aged "molybdenum dlSUl. fide-containing 'sample possessed superior modulu's; tensile and elongation characteristics 'tofieither the-1 1181118X orP-33-bbntaiiningsamples.

7 The butadiene-styrene"rubberdescribed in Exa'mple 1; was compounded'in accordancewitlithe-followingrecipes 40 Flerranriine Stea'ric aci {As in Example I;

F.', and physical properties" determined. f'l he' following results were obtained inftwo difierentcuretim'e's;

Inhehtan; vr -volumeiraetionof polymer ln'swollengel.

employed using .N0.' 2}garnet paper (AS 'llM revised 1946, 1947). Alli'samplesi were =-extrct 7 1 toluene ezeotrope and were then dried lnwaeuum rie week.

'EXAMPL E'ZIH A '71/ 29 butadiene/styrene -gmbber wasgprepared by emulsion polymerization at1122 F: toggive a polymer havinga rawMooney value (-ML-4)3ofkl8%and:a bound "styrene content of 23.'5 ;pjercent.iaAtypicalrecipe for the productionlof'theqpolymenofsthis'type is; as-fqllows-z. I

fable VI Dodecyl e ja tan as 'Y q fi iiforQai IK MH" Stocks were compoundedon 511 mill; curcdiat *3 07* .rPa-rts by. weight The rubber was compounded using molybdenum disulfide, a mixture of molybdenum disulfide and Philolack 0* carbon black, and Philblack 0* carbon black as reinforcing agents. The following compounding recipes were employed:

Table VII Parts by weight "56 3 1. 75 Santocure 1 0.8

1 As in Example I.

The stocks were compounded on a roll mill, cured at 307 F., and physical properties determined. The following results were obtained at two difierent cure times:

Table VIII Cure 300% Elonga- NBS Reinforcing Agent Tim Modulus, Tensile, tion, Abra- Min. p.s.i. p.s.i. percent sion Index Molybdenum disulfide.. 1,330 1,460 370 3.37 Do 45 1, Q0 1, 370 250 2.88 Philblack O-I-MOSz. 15 1,280 2, 600 540 9.05 Do 45 1,380 2, 250 450 7.12 15 1,000 2, 050 500 11.11 45 1, 100 1, 900 440 8. 56

1 As in Example 11.

It will be noted that the sample containing Philblack 0* plus molybedenum disulfide yielded a cured rubber possessing increased tensile and elongation properties as compared to the rubber containing solely Philblack 0* carbon black or molybdenum disulfide.

EXAMPLE IV Molybdenum disulfide was employed as a reinforcingagent for natural rubber (#1, Smoked Sheet). A control run was made using Philblack 0* carbon black as the reinforcing agent. The following compounding recipes were employed.

Table IX Parts by Weight Natural rubben- 100 100 Molybdenum di. 10 140 Philblack O... 50 Zinc oxide--- 4 4 Steuric acid 3 3 Su1fur 2 2 Santocure 1 0.5 0.5 Phenyl-betam onhthylqmine 1 1 1 As in Example I.

The stocks were compounded on a roll mill, cured 30 minutes at 307 F. and physical properties determined. Results were as follows:

Table X Molybdenum Philblack Disulfide O 300% Modulus, psi (80 F.) 1, 870 1, 490 Tensile, p.s.i. (80 F. 3, 150 3, 032 Elongation, Percent (80 F.) 470 470 Swell, l 0. 321 0.300

1 As in Example It.

*Phillips Petroleum Co. trademark; high abrasion furnace black.

It is apparent that the rubber stock containing molybdenum disulfide as the reinforcing agent possesses prop erties which are at least comparable to the rubber stock containing Philblack 0* carbon black.

EXAMPLE V A /25 butadiene/styrene rubber was prepared by emulsion polymerization at 41 F. to give a polymer having a raw Mooney value (ML-4) of 52 and a bound styrene content of 20 percent. A typical recipe for the production of a polymer of this type is as follows:

Table XI Parts by weight But-adiene 75 Styrene 25 Water 180 Rosin soap, K salt 45 Tamol N 0.15 Na PO l2H O 0.80 p-Menthane hydroperoxide 0.12 FeSO -7I-I O 0.20 K P O 0.30

Tert-dodecyl' mercaptan as required for a 52 rubber ML-4.

Sodium salt of a naphthalene 'sulfonic acid condensed with formaldehyde.

The rubber was compounded using as reinforcing agents tungsten disulfide and a medium thermal carbon black l Tungsten disulfide as received was wet ball milled (in water) for 7 days, dried in a vacuum oven, and chunks were crushed. Material crumbled easily. Surface area of product was 2.1 sq. meters/gram.

The amount of WS: employed was equivalent in volume to the 50 parts of carbon black. 7

2 Surface area, 7.5 sq. meters/gram. 3 Physical mixture containing 65 percent of a complex diarylaminelgetone reaction product and 35 percent of N ,N-d.iphenyl-p-phenyleneamine.

4 N-cyclohexyl-Z-benzothiazylsulfenamlde.

The stocks were compounded on a roll mill, cured to as near the same level of crosslinks aspr'acticabl,

and physical properties determined. Results were as follows:

Table XIII Run 1 Run 2 Cure times, minutes 60 30 Cure temperature, F... 307 307 vX10 moles/cc. 1. 95, 1. 68 300% modulus, p s i. 1, 660 Tensile, p.s.i 1, 530 l, 550 Elongation, Percent" 530 530 Sm-tace/volume ratio 15.7 13. 5

1 The density of network chains is related to the number of crosslinks by the function where n is the number of crosslinks, 6 is the density of the polymer, and M is the molecular weight.

2 Amount of surface available for interaction between the reiuforcin agent and rubber. I

These data show that there is an improvement i n modulus when the stock contained tungsten disulfide,

, Whil the ther. p ysical prope t esren ained substantia y 3hr: s ne L XAMRLEIVI- Natural rubber was compounded using as reinforcing agents tungsten disuliide and ;a -medium thermal carbon black (Thermax) as described in Example V. Comrecipes were follows;

The stocks were compounded onajroll mill, cured to as near the same level of cross links as practicable, and physical properties. determined. Results were as follows:

Table. XV,

Run 1 Rim 2 Cure time, minutes 45 27 Cure temperature, F 280 280 10610, moles/ee '1. 15 1. 21 300% modulus, p.s.i 1, 280 840 Tensile, p M r 2, 470 4, 110 Elongation, percent 480 770 Surface/volume ratio 1 15.7 18. 5

V I As in Example V.

The presence of tungsten disulfi'de :substantially'improves the modulus of natural rubber.

EXAMPLE VII The butadiene/styrene rubber described in Example 'Vwas compounded using as reinforcing agents a mixture f :tlmgsten disulfide a high abrasion furnace black (Philblack 0, Phillips Petroleum Co. trademark), and

As in Example V Surtace area, 75.1 sq. meters/gram.

In run '1 the amount of tungsten disulfide added was equivalent in volume to 25 parts of carbon black, thus making the totalvolume of reinforcing agent in run 1 :equivalent to that in-run 2.

The stocks, were compounded on a roll mill, cured to as near the same level of crosslinks as practicable, and physical;properties determined, Resu1ts were as follows: V.

the rubber composition contains from about 25 to about 7 ,25O parts' by weight of molybdenum disulfide per 100 7 T b X W! Cure time, minutes i5 28 Cure temperature, F. 307- 397 I 11x10, moleslce. 1. 1. 68 300% modulus, p.s i 1, 270 1, 850 Tensile, p.s.i.. 050 4,180 Elongation, percent V 66 560' 1 As in Example V.

The furnace black employed is known to be an excellent reinforcing agent for rubber and vwould be expected to be superior to tungsten disulfide since it had a surface area of 75.1 sq. meters/gram while that of the tungsten 'disulfide was 2.1 sq. meters/gram. The data show,

however, that a very good product is obtained when half of the furnace black is replaced by tungsten disulfide,

As will be evident to those skilled in the art, various modifications of this invention can be made, or followed, in the light of the foregoing disclosure, without departing from the spirit or scopcof said disclosure.

- I claim:

1. A vulcanized rubber composition comprisinga rubbery component selected from the group consisting of natural rubber, a homopolyrner of a conjugated diene,

a copolymer of a conjugated diene and a compound containing an active CH =C group which is copolymerizable therewith, said conjugated diene containing at least 4 carbon atoms per molecule, and a reinforcing amount of a sulfide of a group VI-A metal, added'tosaid rubber before vulcanization. I a

2. A composition according to claim'll in which the sulfide is a molybdenum sulfide. Q 3. A rubber compositionaccording to clairnZwherein parts of rubbery component.

4. A rubber composition accordingtto claim 2 wherein V the rubber component possesses a Mooney value (ML-4) in the range from about 10t0' 125. 5. A vulcanized rubber composition comprising arub- .bery component selected from the group, consisting of a :natural rubber, a homopolymer of a conjugated .diene,

a copolymer of aconjugated'dieneand a compound con:

'taining an active CH =C group which is copolymerizable therewith, said conjugated diene containing at least 4 carbon atoms per molecule, and reinforced with a reinforcing amount of reinforcing agent comprising molybdenum disulfide, added to said rubber before vul: canization. V

6. A rubber composition according to claim 5 where? in said reinforcing agent comprises at least. 10 weight per cent molybdenum disulfide, based on the total reinforcing agent, admixed witha mineral pigment.

7. A rubber composition according to claim 5 wherei in said reinforcing agent is molybdenum disnlifide admixed with carbon black. 7

8. A rubber composition according to claim 7 where; in said admixture of molybdenum disulfide and carbon black comprises at least 10 weight percentmolybdenum disulfide based on the saidadmixturel 9. A rubber composition according to claim 5 wherein said reinforcing agent is molybdenum disulfide; 1

10. A rubber composition according to claim 9 wherein. the rubbery component possesses a Mooney value (ML-4) in the range from'about 10 to about 75.

11. A rubber composition according to claim 10 wherem the rubbery component is a'homopolymer of "butadiene. I r 12. A rubber composition according to claim 11 wherein the rubbery component is a copolymer of butadieneand styrene. 7 13. A vulcanized rubber composition comprisingta rubbery component selected from. the group consisting of a natural rubber, a homopolymer of a conjugated diene, a copolymer of a conjugated diene and a compound containing an active CH =C group which is copolymerizable therewith, said conjugated diene containing at least 4 carbon atoms per molecule, .and reinforced with a reinforcing amount of reinforcing agent comprising tungsten disulfide, added to said rubber before vulcanization.

14. A rubber composition according to claim 13 wherein said reinforcing agent comprises at least 10 weight percent tungsten disulfide, based on the total reinforcing agent, admixed with a mineral pigment.

15. A rubber composition according to claim 13 wherein said reinforcing agent is tungsten disulfide admixed with carbon black.

16. A rubber composition according to claim 15 wherein said admixture of tungsten disulfide and carbon black comprises at least 10 weight percent tungsten disulfide based on the said admixture.

17. The process of producing a novel rubber composition which comprises incorporating into a rubber selected from the group consisting of natural rubber, a synthetic homopolymer of a conjugated diene, and a synthetic copolymer of a conjugated diene and a compound containing an active CH =C group which is copolymerizable therewith, said conjugated diene containing at least 4 carbon atoms per molecule, compounding in-, gredients comprising a sulfide of a group VI-A metal,

curing said mixture under curing conditions, and recovering a rubber characterized by improved modulus, tensile and elongation characteristics.

18. The process of producing a novelrubber composition which comprises incorporating into a rubber selected from the group consisting of natural rubber, a

synthetic homopolymer of a conjugated diene, and a synthesis copolymer of a conjugated diene and a compound containing an active CH =C group which is copolymerizable therewith, said conjugated diene containing at least 4 carbon atoms per molecule, compounding ingredients comprising molybdenum disulfide, curing said mixture under curing conditions, and recovering a rubber characterized by improved modulus, tensile and elongation characteristics.

19. The process of producing a novel rubber composition which comprises incorporating into a rubber selected from the group consisting of natural rubber, a synthetic homopolymer of a conjugated diene, and a synthetic copolymer of a conjugated diene and a compound containing an active CH =C group which is copolymerizable therewith, said conjugated diene containing at least 4 carbon atoms per molecule, compounding ingredients comprising tungsten disulfide, curing said mixture under curing conditions, and recovering a rubber characterized by improved modulus, tensile and elongation characteristics.

No references cited. 

1. A VULCANIZED RUBBER COMPOSITION COMPRISING A RUBBERY COMPONENT SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER, A HOMOPOLYMER OF A CONJUGATED DIENE, A COPOLYMER OF A CONJUGATED DIENE AND A COMPOUND CONTAINING AN ACTIVE CH2=C< GROUP WHICH IS COPOLYMERIZABLE THEREWITH, SAID CONJUGATED DIENE CONTAINING AT LEAST 4 CARBON ATOMS PER MOLECULE, AND A REINFORCING AMOUNT OF A SULFIDE OF A GROUP VI-A METAL, ADDED TO SAID RUBBER BEFORE VULCANIZATION. 